Regenerative piano



Jan. 10, 1933.

.1. H. HAMMOND, JR 1,893,940

REGENERATIVE PIANO Original Filed July 24. 1926 4 Sheets-Sheet. l

wanm ymdfi Jan. 10, 1933. J. H. HAMMOND, JR

REGENERATIVE PIANO 1926 4 Sheets-Sheet 2 Original Filed July 24 WWII/WWWJim. 10, 1933. J. H. HAMMOND, JR

REGENERATIVE PIANO Original Filed July 24. 1926 4 Sheets-Sheet 3 A M i iy 1 i l i i 1 M 0 1 y i W i y i l M Jan. 10, 1933. J. H. HAMMOND, JR

REGENERATI VE- PIANO Original Filed July 24, 1926 4 Sheets-Sheet 4Patented Jan. 10, 1933 UNITED STATES PATENT OFFICE BEGENERATIVE PIANOApplication filed July 251, 1926, Seria1 No. 124,576. Renewed April 6,1932.

This invention relates to musical instruments and more particularly tohigh power sound producers.

The invention has reference to a musical instrument of the typeproducing damped compressional waves and relates to means for increasingthe energy impressed upon said waves.

A feature of the invention relates to the provision of a reverberatoryelement adapted to emit compressional Waves in combination with meansfor impressing upon the element energy having a predetermined frequencyand a sound sourcetuned to the pre- 13 determined frequency forcontrolling the energy impressed upon the reverberatory element. I

A feature of the invention relates to the provision of an amplifyingdevice having its :3 input connected so as to be controlled by arelatively low power source of sound, and its output directly connectedto a reverberatory element positioned adjacent said sound source.

3 Other objects will appear from the following description taken inconnection with the accompanying drawings, in which Figure 1 is a topplan view of one embodiment of the invention;

Figure 2 is a front elevation of the device of Fig. 1;

Figure 3 is a diagrammatic showing of a portion of the structure ofFigures 1 and 2 in combination with an amplifying device;

Figure 4 shows a modified form of the reverberato-ry element of Fig. 3;

' Figure 5 shows another modification;

Figure 6 shows an electro static device for actuating the reverberatoryelement of the device;

Figure 7 shows an electro magnetic device actuated by the tune-delement.

Like reference characters refer to like parts in the several figures ofthe drawings.

parts will be identified by specific names for convenience of expressionbut they are intended to be as generic in their application to similarparts or equivalent construction as the art will permit.

In the following .description and claims,

Referring to the drawings and more particularly to Figures 1 and 2thereof, there is shown a musical instrument of the form of a grandpiano and includes a casing 10 having an upper apertured wall 11, and alower apertured wall 12. l/Vithin the casing 10 there is provided afixed metal frame 13 for supporting a plurality of tuned vibratoryelements or strings such as 14 for producing sound.

A sounding board 15 is positioned adjacent said strings, and forms areverberatory element energized by compressional waves emitted from thestrings. For actuating the strings tuned to a note of the musical scale0 l u I there 18 provided a percussion mechanism ineluding a hammer 16,each actuated through an operative connection of conventional form by.means of a key such as 17 included in a manual 18 ofthe piano.

The instrument is provided with usual pedals, such as a piannissimopedal 20, a sostenuto pedal 21 and a fortissimo pedal 22 of conventionalconstruction, but as these form no part of the present invention, it isthought that no further description thereof 70 is required. Theinstrument may also be provided with controllable closures for theapertures of the upper wall 11 of the casing 10 and for the lower wall12. These closures may take the form of pivotally mounted modulat- S0ing reflectors 23 for variably controlling and reflecting the soundwaves emitted from the instrument. Each reflector may further beprovided with a thin sheet of metal 24: on the inner face thereof, andmay also include a layer of substantially sound insulating ma terial 25.The side walls of the casing may also be provided with a layer26 ofsound insulating material for limiting the sound. The reflectors 23 ofthe upper group are provided with integral arms 27 respectively, theouter ends of which are pivotally connected to a rod'28. A link 29 (seeFig. 1) operatively interconnects the rod 28 to a radial arm 30 which issecured to a vertical rotatable shaft 31 as by being pinned thereto. Theshaft 31 is journalled' in spaced bearing plates 32, 32, secured to thecasing 10. Similarly the reflectors of the lower group are provided withintegral arms 33, respectively, the outer ends of which are pivotallyconnected to a bar 34. A l1nk 35 operatively interconnects the bar 34tag a second radial arm 36 secured to the shaft For operating themodulating reflectors to 42 is pivoted to a portion of the casing 10 asp at 43, and its other end is engaged by a rod fied, and their I toterminal posts 55 and 56.

- netic material attached to the 44 connected to the rear end of arocking pedal 45 mounted adjacent the pedals 20, 21, 22. A retractilespring 46 serves to maintain the pedal 45, the reflectors 23, and theassociated parts, in the position shown in Figs. 1 and 2, with thereflectors open and the pedal up. f

The portion of the instrument so far described may be operated toproduce damped compressional waves. For example, when a key 17 isdepressed, the hammer 16 strikes the respective tuned vibratory element.The waves thus set up, set the sounding board 15 into vibration. Thesounding board is relatively large, and. in contact with a considerableamount of atmospheric medium, and thus eilectively emits the energy ofthe waves into the surrounding medium. The waves actually emitted fromthe interior. of the casing may be limited in amplitude, and effectivelycontrolled to produce desirable effects, by the use ofthe fourth pedal45 for that purpose.

The damping of the waves may be modiamplitude :considerably increased byimportant features of the invention which will now be described- Thismech anism includes-means for impressing high power energy upon thereverbatory element. The embodiment shown in Fig. 3 comprises arelatively small light sheet 50 of paramagsounding board 15 near thecenter thereof, and on a face opposite that which is proximate the thusto one terminal of thefilament 82. The

strings, and acted upon by an electromagnet 51, having a coil or winding52. The arrangement is such that oscillatory energy applied to themagnet winding 52 acts upon the sheet 50 as an armature, and impressesthe energy upon the reverbatory element 15. The ends of the winding 52pf the magnet 51 are connected respectively by conductors 53, 54

For controlling the operation of the high power energy means, thereisprovided a metal plate 60 (see Figs. 1 and-3) afiixed to the wall 11 andin spaced relation with the tuned strings 14. The plate 60 is placedclose to the strings, thereby even when the strings are actuated withconsiderable force. mounted-ion insulating blocks'such as 61 (see theamplifier is of the grid resistance 98 and to the stat 102, als but notso close as to be contacted The plate 60 is terminal of which isconnected by a conductor F 3) so as to be electrically insulated fromother part's'of the instrument. The plate 60 is connected byan'electrical conductor 62 to one pole of a direct current source 63 ofelectric potential, the other pole of which is connected through acondenser 64 to one end of a Winding of a potentiometer 65, the otherend of which is connected by conductor 66 to the string supporting frame19 of the piano, and by a conductor 67 to a terminal post 68, conductor69 to ground at 70. The winding of the potentiometer is engaged by aslider 71, which is-mounted on, but insulated from, a collar 7 2. Thecollar 72 is adjustably fixed upon the shaft 44. The slider is connectedby a flexible conductor 73, and conductor 74 to a terminal post 75.

For amplifying the energy produced by striking the strings 14, there isprovided an amplifier 80, shown within the dash-dot line 81 of the lowerportion of Fig. 3. As shown coupled type. .Each stage includes a threeelectrode amplifying vacuum tube, preferably of the type having a highmutual conductance, and it is thought that a description of one willsufiice for all. Each tube comprises a heated filament 82 for emittingelectrons, a grid 83 for controlling the passage of electrons, and aplate 84 on which the electrons impinge.

A detailed description of the amplifier 80 will now be given. The

terminal post is connected by a conductor 90 to one terminal of ashunting or grid leak resistance 91 and to tube 92 of the first 83 ofvacuum stage. The other terminal of the resistance .91 is grounded, Theplate 84 of the first stage tube 92 is connected to one terminal of i aplateresistance 93 the other terminal of which is connected by aconductor 94 positive pole of a high voltage source of electromotiveforce, such as a battery 95 for applying a positiveeleetric potential tothe plate 84 with respect to the filament 82. The negative pole of thebattery 95 is connected to a common filament return conductor 96 andplate 84 is also connected through a condenser 97 to one terminal of ashunting or grid leak grid of vacuum tube 99 of the second stage. Theother terminal of the resistance 98 is connected to-the nega tive poleof a low voltage source 98' of electric potential, the other pole ofwhich is second stage tubes 92, 99 are connected across the four stage,resistance to the afilament heating battery 100, there being rheostat101 a d for the tube 99 a series rheo djustable, for controlling thefilament heating currents. The plate 84 of the second sta e tube isconnected to one terminal of a p ate resistance 103, the other providedfoil-file tube 92 an adjustable series 104 to the positive pole of thebattery 95, whereby a high positive potential is applied to the plate ofthe tube 99 with respect to its filament. The plate of. the tube 99 isalso connected through a condenser 105 to one terminal of a shunting orgrid leak resistance 106 and to the grid of vacuum tube 107 of the thirdstage. The other terminal of the resistance 106 is connected by aconductor 108 to the negative pole of a biasing battery 109, a by passcondenser 110 being provided in shunt with the battery, The positivepole of the battery 109 is connected to one pole of a filament heatingbattery 111, which is also shunted by a by pass condenser 112. The plateof the tube 107 is connected to one terminal of a plate resistance 113,the other terminal of which is connected by a conductor 114 to thepositive pole of a source of direct current such as a battery 115, theother pole of which is connected to a common filament I return conductor116 and thus to one terminal of the filament of the tube 107. The comductor 116 is grounded to the ground 70. The battery 115 is shunted by aby pass condenser 117. The plate of the tube 107 is also connectedthrough a condenser 118 to one terminal of a shunting or grid leakresistance 119 and to the grid of vacuum tube 120 of the fourth stage.The other terminal of the resistance 119 is connected to the negativepole of the biasing battery 109. The filaments 82 of the third andfourth stage tubes 107 and 120, are connected across the battery 111,there being provided for the tube 107 an adjustable series rheostat 121,and for the tube 120 a similar rheostat 122 for controlling therespective filament heating currents. A by pass condenser 123 isconnected from the tube 120 is connected by a conductor 124 to theterminal post'55, the circuit extending thence, conductor 53, winding52, conductor 54, terminal post 56, and over a conductor 125 to thepositive pole of the battery 115, whereby-a high positive potential isapplied to the plate of the tube 107. The plate 60 and the amplifyingmeans 80 thus operatively interconnect the sound source 14 and theemitting sounding board 15.

In the modified embodiment shown in Fig. 4 a separate sounding board 200is mounted in the casing 10. For applying amplified energy thereto anoscillating device is provided, including a tube 201, preferably ofcopper, which is attached to the sounding board 200. Around thetube 201there is mounted an annular magnet 202 formed of soft iron, having awinding 203 recessed therein. A source of direct current 204 isconnected across the terminals of the winding 203, for energizing thewinding, and thus producing a magnetic field of constant polarity aboutthe cylinder 201. Within the tube 201 there is provided a sec- 0ndannular magnet 205, the terminals of the conductor 108 to ground. Theplate of i board, thus improving the effect. The mag net windings 52 areconnected in multiple, and to the terminal posts 55, 56, which areconnected to the amplifier 80 in the same manner as is shown withrespect to the terminal posts 55, 56 of Fig. 3.

The modified form shown in Fig. 6 shows electrostatic means forimpressing amplified energy upon the sounding board. In this embodimenta conducting plate 210 is ailixed to a face of the sounding board 15.Adjacent to, and slightly spaced from the plate 210 is a fixed plate 211mounted upon spaced brackets 212, 212, and adjustable as by thumb nuts21.3. The fixed plate 211 is connected by a conductor 214 to oneterminal of a resistance or impedance 215 and to the terminal post 56.The sounding board plate 210 is connected through a condenser 216 to theother terminal of the resistance 215 and thus to the terminal post 55.The terminal posts 55 and 56 are connected to the amplifier 8 0 in thesame manner as is shown with respect to the terminal posts 55, 56 ofFig. 3.

The modified form shown in Fig. 7, may housed instead of thecapacitative form of pickup shown in Fig. 3. In this embodiment, thereis shown a bracket 220 extending across the interior of the casing 10instead of, and in the same manner as, the plate 60 of Fig. 3. Thebracket 220 is itself, however, inactive, serving only as a support.Mounted thereon is a plurality of angles 221 each supporting amagnetized core 222, having both ends 223 turned into proximity with thetuned string 14. lVound on the core 222 is a coil 224 of insulated wire.It is understood that one such core and coil is provided for each 'noteof the musical scale of the instrument, and positioned adjacent thetuned elements corresponding to the notes, respectively. The coils areconnected in multiple, and to conductors 225 and 226. The conductor 226extends to one terminal of the potentiometer winding 65, the otherterminal of which is connected to the conductor 225 and also to theterminal post 68. The slider 71 is connected by conductors 73. 74 to theterminal post 75. The terminal posts 68 and 7 5 are connected to theinput of the amplifier 80 as in the manner shown in Fig. 3.

In the operation of the instrument with the amplifier 80 in action, whenthe musician strikes a key 17 to actuate a hammer 16 to and-thevibrating string at a'frequency depending upon thefrequency of vibrationof the string. This change incapacity changes the charge on thecondenser 64, and thus changes the potential on the grid 83 of thewaves, comprising a source ofsound, a revertube 92 with respect toground. The changes in potential modify the space current'of the tube,and there appear in the plate circuit amplified unidirectional impulseshaving frequencies determined and controlled by the vibration of thestring. These impulses are further amplified bythe second, third, and

- board 15 causing it fourth stages, and thus energy of. greatlyincreased power, but of like frequency, is producedby the amplifier.This energy is impressed by the magnet 51 upon the sounding to emitcompressional waves of great intensity.

It will be noted that some of the energy emitted by the sounding board15 is fed back to the string, and thus a regenerative effect of greatvalue in controllingthe decrement of the waves is secured. By varyingthe positionof the slider 71by the foot, the musician can vary'thedamping, and the amplitude of the sounds as desired. Furthermore. byvarying the position of the modulating reflectors 23 the sound may bevariably controlled.

The operation of the modified form of Fig. 4 is similar to that ustdescribed, theenergy of the output of the amplifier 80 being applied tothe magnet 205, to set up an alternating field of force. The directcurrent field set up by the magnet 202 thus causes the tube 201 tovibrate in accordance with the oscilla- 'tions of the current traversingthe coil 202, and the vibrations are thus applied to the sounding board200.

210, 211 are correspondingly varied.

cordingly changes in attractive force betwe en' "Fig. 6, when the Theoperation of the embodiment of Fig.

5 will, it is thought, be obvious, from the foregoing description, itbeing understood that, the energy is impressed upon the sounding boardat a variety of points therein.

In the operation of the embodiment of potential across the terminalposts 55. 56is varied by the operation of the amplifier 80, the chargeson the plaice these plates occur, causing relative movement of theplates. The plate 211 is fixed. and thus the plate 210 is moved,carrying with it the portion of the vibration of the sounding board.

- The operation of the embodiment shown in Figure 7 is similar to thatdescribed in connection Iwith Figure 3, except that the change inpotential on the grid 83 of the tube 92', is caused by current inducedin the pickup coil 224 by variations in its magnetic field of force.

The invention on which this application is 'tatably positioned bratingsaid element, means of relatively low power including tuned vibratorydevices arranged adjacent said reverberatory element, a source of highpower energy,.controlled by said'vibratory devices for actuating thehigh power vibratory means, and movable modulating reflectors in a wallof said casing for controlling the emission .of. sound from theinstrument.

3. A musical instrument comprising 2. casing, a sounding board withinsaid casing, means of relatively high power for vibrating said board,means of relatively low power including tuned vibratory devices arrangedadjacent said sounding board, a source of high power energy controlledby said vibratory devices for actuating the high power vibratory means,modulating reflectors roin a wall of the casing to limit the amplitudeof sound emitted therefrom, and means controlled at the will of anoperator for actuating said reflectors.

4. A musical instrument comprising a casing having apertures, in thecasing, means of relatively'high power for vibrating said-board, meansof relatively low power including tuned strings arranged adjacent saidsounding board, a source of high power energy controlled by said stringsfor actuating the high power vibratory means, controllable closures inthe apertures of said casing, and a pedal operatively connected to saidclosures.

5. A device for producing compressional waves, comprising a casinghaving apertures,

a source of sound within said casing, a reberatory element adjacent saidsource, a

source of'energy controlled by said source a sounding boardwithforvibrating said element at the frequency of the sound wavesproduced by said source, and means for mechanically limiting the soundemitted through the apertures of said casing.

7. A musical instrument comprising a casing'having apertures, areverberatory element positioned .within the casing, means of high powerfor impressing energy upon said element, means of low power includingtuned vibratory devices arranged adjacent said reverberatory element, asource of energy con trolled by said vibratory devices. for actuatingthe high power energy impressingmeans, and mechanical means for limitingthe volume of sound emitted through said apertures.

8. A musical instrument comprising acasing, a sounding board positionedwithin said casing, means of high power for impressing energy upon saidboard, means of low power including tuned vibratory devices arrangedadjacent said sounding board, a source of energy controlled bysaid'vibratory devices for actuating the high power energy impress ingmeans, and means for variably controlling the volume of sound emittedfrom'the interior of the casing.

9. A musical instrument comprising a sounding board means of high powerfor impressing energy upon said'board, means of low power includingtuned strings arranged adjacent said sounding board, a source of energycontrolled by said strings for actuating the high power energyimpressing means,

' and means controlled, at the will of an operator -for variablycontrolling the energy produced by said source.

10. A device for producing compressional waves, comprising a source ofdamped compressional waves, ,a reverberatory element adjacent saidsource for emitting compressional waves, sound amplifying meansinterposed between said source and said reverberatory element, andelectrical means for controlling the effectiveness of said last namedmeans. Y

11.' A device for producing compressional waves, comprising a source ofsound, a reverberatory element adjacent said source, a

source of energy controlled by said source for impressing upon saidelement energy of the frequency of the sound waves produced by saidsource, and means controlled at the will of an operator for controllingthe effectiveness of said energy impressing source.

12. In a piano having a plurality of strings and a sound board, meansfor picking up vibrations from one of said elements, amplifying saidvibrations and applying the amplified vibrations to the other of saidelements, whereby the damping of the vibrations of said strings may bedecreased at will and mechanical regeneration maybe obtained.

13. In a system of piano amplification, an electro-acoustic closedcircuit, said circuit being adapted to derive energy from one vi?bratory part of said piano, amplify said energy and return the amplifiedenergy to another vibratory part of said piano which is acousticallycoupled to said first part.

14. A system of'amplifying musical tones in which a loud speakerproduces mechanical vibrations in a sound board which in turn modifieselectrical currents which are amplified and returned to the loud speakerfor actuating the same. I

15. A system of piano amplification in which mechanical vibratory energyis transformed into corresponding electrical vibratory energy, amplifiedand retransferred to the piano in the form of vibratory mechanicalenergy.

16. In a piano having strings and a sounding board acoustically coupled,means for increasing the effective coupling comprising electrical meansfor picking up energy fromv said strings, amplifying said energy andapplying the amplified energy to said sounding board.

17. In a piano having strings and a sounding board, a loud speaker unithaving a vibratable element, said element being directly secured to saidsounding board, means for modifying electrical energy in accordance withthe variations of said strings, means for amplifying said energy andmeans for operating said loud speaker unit in ac cordance with saidamplified energy.

18. In a piano having a vibrating system, a pedal for normallycontrolling the volume of sound emitted therefrom and means foramplifying the energy of said system, said means being controlled by theposition of said pedal. p v

19. In combination, a piano having parts adapted to vibrate at dilferentfrequencies, a pick-up device for picking upsaid frequencies, a soundpropagating element, amplifying means between said pick-up device andsound propagating element, and regenerative means to feedback energyfrom the output of said amplifying means to its input. a

20. In combination, a piano having parts adapted to vibrate at diiferentfrequencies, a pick-up device for picking up said frequencies, a soundpropagating element, amplifying means between said pick-up device andsound propagating element, and regenerative means to feed back energyfrom the output of said amplifying means to its input and means forvariably controlling energy between said pick-up device and soundpropagating element.

21. In a piano, a plurality of strings tuned to different frequencies, asound propagating element,- a plurality of electro-mechanical pick-updevices, one for each string, for separately directly picking up thevibrations of the different strings and electrical amplifying devicesbetween said pick-up devices and said sound propagating element.

22. In a piano having strings adapted to vibrate at differentfrequencies, a plurality of separate pick-up dev ces for said strings topick up different frequencies directly therefrom, a sound propagatingelement and amplifying means between said pick-up devices and soundpropagating element.

23. In a piano having parts adapted to vibrate at different frequencies,a plurality of separate pick-up devices for said parts to pick updifferent frequencies, a sound propagating element and amplifying meansbetween V said pick-up devices and sound propagating element.

24. In a piano having parts adapted to vibrate at different frequencies,a sounding board, a pick-up device for picking up said frequencies, aplurality of separate receiving units applyin sound energy 'to saidsounding board, ampli ying means between said pick- .up device andseparate receiving units, and

regenerative means to feed back energy from the output of saidamplifying means to its input. 7

Signed at New York in the county of New York and State of New York this16th day of July A. D. 1926.

JOHN HAYS HAMMOND, JR.

